Redfield ratio

The Redfield ratio is an important idea in ocean science. It talks about the steady balance of three key elements—carbon, nitrogen, and phosphorus—that are found in tiny sea plants called marine phytoplankton and deep in the oceans.

This idea is named after Alfred C. Redfield, an American oceanographer. In 1934, he noticed that these elements appeared in a fairly regular pattern in samples he collected during many trips on the research ship Atlantis. He found that for every 106 parts of carbon, there were about 16 parts of nitrogen and 1 part of phosphorus. This pattern is called the C:N:P = 106:16:1 ratio.

Even though scientists have found some differences depending on where they take their samples or which tiny plants they study, the Redfield ratio is still very useful. It helps scientists understand how nutrients affect plant growth in the ocean. Newer studies using data from after the 1970s show the average ratio is closer to 163:22:1, showing that these numbers can change over time and in different parts of the sea.

Discovery

Alfred Redfield studied data about important nutrients in the Atlantic, Indian, Pacific oceans, and the Barents Sea for his 1934 paper. He was a scientist who traveled on a research ship called Atlantis and looked at the amounts of carbon, nitrogen, and phosphorus in tiny ocean plants called plankton.

Redfield found that the ratio of nitrogen to phosphorus in seawater was almost always the same, close to 16 parts nitrogen to 1 part phosphorus. He thought there were two reasons for this pattern. First, tiny ocean plants change to match the nutrients around them. Second, natural processes help keep the nutrient levels balanced in the water. Later, in 1958, Redfield suggested that the way nitrogen and phosphorus cycle through the ocean helps keep this balance.

Explanation

Alfred Redfield noticed that the chemistry of the deep ocean matches the chemistry of tiny plants called phytoplankton in the surface ocean. Both have a ratio of nitrogen to phosphorus of about 16 to 1. In most phytoplankton, the ratio of carbon, nitrogen, and phosphorus is about 106:16:1 when they have enough nutrients.

Experiments show that phytoplankton keep this ratio even when there is more than enough nutrients around. This suggests that they adapt to the ocean's nutrient levels in a special way. In the ocean, many tiny plants have a lot of nitrogen. When these plants are eaten by other tiny plants, they keep a similar ratio of nitrogen to phosphorus. When these plants sink deep into the ocean, bacteria break them down and release nutrients like carbon dioxide, nitrate, and phosphate back into the water. The way these nutrients move and mix in the ocean helps keep the ratio of nitrate to phosphate almost the same everywhere. Phytoplankton help keep this balance by using extra phosphorus and making more nitrogen when needed.

Uses

The Redfield ratio helps scientists understand how carbon and nutrients move in the oceans. It is used in models that study the world's climate and can show which nutrients are missing in certain areas. This ratio also helps explain why some areas have lots of tiny plants in the water and can even affect the amount of oxygen underwater.

Scientists think this ratio might also work for plants and soil on land, which could help us learn more about what plants need to grow well.

Deviations from the canonical Redfield ratio

The Redfield ratio was first found by looking at tiny plants in the water, called plankton, and the nutrients in the Atlantic Ocean. Many more tests later supported this idea. But, when scientists grew different kinds of plankton and limited their food, they saw that the amount of certain nutrients could change a lot.

Even though the Redfield ratio stays about the same deep in the ocean, the tiny plants can change how much of each nutrient they have. This change depends on how fast they grow and what kind of tiny plants are there. When there isn’t much of one nutrient, like phosphorus, the tiny plants can change to use less of it. This shows that the Redfield ratio might just be an average for today’s oceans, not a fixed rule for all tiny plants. Still, the idea of the Redfield ratio helps scientists understand how nutrients work in the sea.

Extended Redfield ratio

Some scientists think that other elements like potassium, sulfur, zinc, copper, and iron are also important in ocean chemistry.

In particular, iron (Fe) was thought to be very important because early biological oceanographers believed it might limit primary production in the ocean. Experiments later showed that iron does help plants in the ocean grow. Adding iron-rich solution to a large area of the ocean increased plant growth. Because of this, scientists created an extended Redfield ratio that includes iron. This new ratio is 106 C:16 N:1 P:0.1-0.001 Fe. The wide range for iron is because ships and equipment can add extra iron to samples, making it hard to measure accurately.

Diatoms, a type of ocean plant, need silicic acid to build their frustules (cell walls) from biogenic silica. For this reason, another ratio called the Redfield-Brzezinski ratio was suggested for diatoms, which is C:Si:N:P = 106:15:16:1. It has also been found that the amount of oxygen used by these plants follows a pattern with other elements, with the O₂:C ratio measured at 138:106.